Electric discharge device



Nov. 10, 1936. P. LE NZ ELECTRIC DISCHARGE DEVICE Filed Nov. 29, 1932Fig.5.

I I I I u I I I I n 7.

Inventor: Paul Lenz,

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cam 00 5 Patented Nov. 10, 1936 UNITED STATES.

PATENT OFFICE ELECTRIC DISCHARGE DEVICE Paul Lenz, Berlin-Grunewald,Germany, assignor to General Electric Company, a corporation of New York8 Claims.

The present invention relates to electric discharge devices, moreespecially to tubes of the hot cathode type.

In the case of hot cathode tubes, particularly those of the larger typeprovided with indirect heating, a comparatively long time is necessaryto bring the cathode to the working temperature after switching on theheating current.

An object of the present invention is to reduce the time necessary forthis purpose. This object is attained in brief, according to the presentinvention, by initially applying to the cathode a higher voltage orcurrent than is normally used. When the working temperature of thecathode is reached or even before that time, if desired, the heatingcurrent automatically is reduced to the normal operating value. Theimproved operation not only offers the advantage that the heatingup timeis considerably shortened over the prior art methods but also in thecase of arc discharge tubes containing vapor or gas, the vapor pressurenecessary for operation is more quickly attained. Different arrangementsmay be employed for carrying out this process and a few exemplary Qembodiments are shown in the drawing. Fig. 1 illustrates an applicationof the invention to a filament energizing circuit which includes aresistance, while Fig. 2 depicts the invention as applied to analternating current circuit containing a transformer. Figs. 3 and 4 showfurther embodiments of the invention in connection with indirectlyheated cathodes.

Referring to Fig. 1, numeral l designates the envelope of an electrondischarge device containing a filament 2, an anode 3 and anelectrostatic control member or grid 4. The filament 2 may constitutethe cathode of the device or in the case of an indirectly heated cathode(not shown), may comprise the heater. The circuit for energizing thefilament 2 includes a source 5 of direct current in series with aresistance 6. In this circuit, there is a starting switch I, also aswitch 8 which controls a short circuit across a portion of theresistance. Switch 8 normally is closed, as indicated. In accordancewith the present invention, there is also provided in this circuit,either in series or in shunt thereto so as to be energized by the samesource of current 5 as energizes the filament 2, a time switch or relay9, the armature of which is mechanically connected in any suitablemanner to the switch 8. The purpose of this relay will be explainedpresently.

As stated hereinbefore, it is desirable in many cases, particularly inpower tubes employing indirectly heated cathodes of large metal content,

to bring the filament up to the normal operating temperature as soon aspossible, thereby minimizing the time during which the tube is unable totake the load. When the cathode is to be initially heated, the switch Iis closed and current from the source 5 flows through the lefthandportion of resistance 8, through switch 8 and the filament, back to thesource. The time device 9 is also energized. The amount of heatingcurrent flowing through filament 2 is determined by the energizedportion of the resistance. This current exceeds the normal heatingcurrent so that the filament temperature increases rapidly. The timerelay 9 which is energized simultaneously by the closing of the switch1, opens the switch 8 after a predetermined time so that the righthandportion of the resistance 6 is inserted into the heating circuit,causing a decrease of heating current. It is apparent that the amount ofoverheating may be controlled accurately by the setting of the timerelay and adjusting the position of the tap on the resistance 6.

In Fig. 2, the filament 2, which may also be a cathode or the heater ofa cathode, is supplied with alternating current from a source ID througha transformer I l of a voltage step-up or 1:1 ratio type. A tap may bebrought out from one of the turns on the transformer primary to acontact 12 disposed adjacent to a contact l3. The latter is connected toan end terminal of the primary winding. There is a pivotally mountedarmature I4 which moves between these contacts, said armature beingconnected to a source of current l0 through a switch 1. A time relay 9is connected across the energizing circuit as in Fig. l, and thearmature of the relay is mechanically connected in any suitable mannerto the armature I4. It is apparent that as the switch 1 is closed withthe armature in its upper position as shown, i. e. against the contactI2, the turn ratio of the transformer H is determined by the number ofturns between the tap and the upper end of the primary. In the case ofstep-up voltage ratio, a voltage is obtained across the secondary, henceapplied to the filament 2, which is greater under these conditions thanif the armature M were making contact with the contact l3. The timerelay 9 is also energized simultaneously when the switch I is closed.This relay operates after a predetermined time interval to cause thearmature to drop back and strike the contact l3. The number of turns inthe primary of the transformer l l is thus increased and thetransformation ratio correspondingly decreased so that the voltageapplied to the filament is reduced. As explained in connection with Fig.1, the amount of overheating and the time duration may be controlled bythe setting of the time relay, and in the case of a transformercoupling, by the proper determination of the tap position on the primarywinding. It is apparent that in the case of a voltage step-downtransformer, a tap may be brought out from the secondary winding insteadof the primary winding and connected to a suitable arrangement ofcontacts. In all cases, the heating current is maintained above itsnormal value for a predetermined time interval and then automaticallyreduced to its normal value. If desired, both the primary and thesecondary windings may have taps simultaneously controlled by suitablyarranged armatures, actuated by a time relay.

Instead of the time relay, there may be employed a thermostatic relayresponding directly to the temperature of the filament. The switchingover from the greater heating current to the normal current then takesplace, not after the expiration of a certain time, but after apredetermined rise in temperature of the filament or cathode. In thiscase, several tube constructions are possible. For example, there may beemployed an additional filament which is the thermal duplicate of thefilament 2 and which when heated in any suitable manner, operates athermostatic switch for causing the required reduction of heatingcurrent supplied to the filament proper. Furthermore, the light givenoff by the main or duplicate filament may be directed onto aphoto-electric tube or a thermo-electric element and cause the necessaryswitching-over of the heating current, using amplifying tubes, ifnecessary.

In the case of indirectly heated cathodes, the construction of thefilament itself may be modilied to facilitate the heating-up process.Thus in Fig. 3 there is shown a metal cylinder l6 coated withelectron-emitting material I! and containinga filamentary heater I8securedat one end to the top of the cylinder. Leads are brought out fromthe free end of the filament, also from an intermediate tap, and fromthe cylinder I6. These leads are connected through relay contacts l2 andI3 to the source i0 in-the same manner as the leads from the primary ofthe transformer in Figure 2. During the preliminary heating-up period,current may be caused to fiow through the intermediate tap instead ofthe end terminal, the resistance of the filament being temporarilyreduced in order to increase the current through the heater. After atime interval determined by a time relay, the connection to theintermediate tap is automatically broken and the entire length of thefilament is connected to the energizing circuit, thereby reducing thecurrent through the heater.

Fig. 4 shows the use of a plurality of filaments which may be operatedin various ways to increase the initial heating-up of the cathode duringthe preliminary period. These filamentary heaters may have different orthe same resistances and may be operated either separately or togetherunder the control of a suitably arranged time relay so that any desireddegree of current increase during the heating-up period may be obtained.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. In combination, an electron discharge device comprising a pluralityof electrodes including a filament, means including a source of ourrentfor initially applying to said filament a voltage greater than thenormal operating voltage, and means including a relay energized by saidsource for reducing the voltage applied to said filament to the normaloperating voltage, said relay having an inherent time delaycharacteristic and when energized, operating after a predeterminedlength of time depending on its inherent time delay characteristic tocause the said reduction of filament voltage.

2; In combination, an electron discharge device comprising a pluralityof electrodes including a filament, a circuit for energizing thefilament, said circuit including a source of current and a resistance,means including a relay having an inherent time delay characteristic inthe energizing circuit for automatically changing the amount ofresistance after an interval determined solely by the time delaycharacteristic of said relay whereby the voltage applied to the filamentfrom said source is changed.

3. In combination, an electron discharge device comprising a pluralityof electrodes including a filament, a circuit for energizing thefilament, said circuit including a source of current and a resistance,said resistance being in series with the current source and filament,means including a relay having an inherent time delay characteristic inthe energizing circuit for effectively removing a portion of saidresistance during an interval determined solely by the time delaycharacteristic of said relay whereby the voltage applied by the currentsource to the filament may be held temporarily above the normaloperating value and after said time interval is automatically reduced tothe normal Value.

4. In combination, an electron discharge device comprising a pluralityof electrodes including a filament, a circuit for energizing thefilament, said circuit including a source of alternating current and atransformer, means including a relay having an inherent time delaycharacteristic in said circuit for changing the voltage ratio of thetransformer, said means operating to provide a voltage across thefilament greater than the normal voltage and after a predetermined timeinterval determined solely by the time delay characteristic of saidrelay, automatically to reduce the filament voltage to the normal value.

5. In combination, an electron discharge device comprising a pluralityof electrodes including a filament, a circuit for energizing thefilament, said circuit including a source of alternating current and atransformer having primary and secondary windings, relay means having aninherent time delay characteristic in the primary circuit forautomatically changing the number of turns in the primary winding of thetransformer after a predetermined time interval determined solely by thetime delay characteristic of said relay means whereby the turn ratio ofthe transformer and the voltage applied to the filament are changed at apredetermined time after the filament is energized.

6. In combination, an electron discharge device comprising a pluralityof electrodes including an indirectly heated cathode, a filamentaryheater for said cathode, a circuit for energizing said filament, meansincluding a relay having an inherent time delay characteristic andoperating after a predetermined time interval determined by the saidtime delay characteristic for increasing the length and resistance ofthe heater whereby the heat given off by the heater is automaticalyreduced.

7. In combination, an electric discharge device comprising a pluralityof electrodes including a filament, means including a source of electricenergy for causing an initial flow of filament current greater than thenormal operating current, and means including a relay energized by saidsource for reducing the current flowing in said filament to the normaloperating current, said relay having an inherent time delaycharacteristic and when energized, operating after a predeterminedlength of time depending on its inherent time delay characteristic tocause the said reduction in filament current.

8. In combination, an electric discharge device comprising a pluralityof electrodes in cluding a filament circuit, means including a source ofelectric energy connected to said filament circuit, said means being soadapted and. arranged that an abnormal wattage is initially consumed insaid filament circuit, and means including a relay energized by saidsource for reducing the wattage consumed in said filament circuit to thenormal operating wattage, said relay having an inherent time delaycharacteristic and when energized, operating after a predeterminedlength of time depending on its inherent time delay characteristic tocause the said reduction of wattage consumed in said circuit.

PAUL LENZ.

